Animal litters containing fuller's earth clays are well known in the art. More particularly fuller's earth clays are comprised of the clay minerals attapulgite, bentonite or various other alumino silicates and have been used in connection with animal litters, alone or in combination with other substances. Attapulgite is a clay mineral whose major constituent is attapulgite. It may also contain varying amounts of other clay minerals such as calcium montmorillonite and sepialite. Attapulgite clay is relatively expensive. Bentonite is a clay mineral that consists principally of sodium and/or calcium montmorillonite and lesser amounts of other clay minerals. The sodium form occurs in the western U.S. and calcium form occurs chiefly in the midwest and southern United States of America.
In most applications, the fuller's earth clay is calcined (dried) by heating it to a finishing temperature of more than 180.degree. C. to remove all of the free moisture and a portion or all of the interstitial moisture of the clay. The advantage of calcining the fuller's earth clays to above 180.degree. C. for use an animal litters is that this hardens them so they do not form dust by the particles abrading against each other. In the case of attapulgite, clay heated to a finishing temperature higher than 180.degree. C. but less than 1000.degree. C. is called fully calcined and is known as a lower volatile material ("LVM") clay. Such clay has no free moisture but some interstitial moisture. Fuller's earth clays which are calcined by heating them to a finishing temperature of more than 180.degree. C. are non-colloidal. Non-colloidal clays are those that do not form colloids when dispersed in a liquid environment such as water.
One disadvantage of the above described calcined, non-colloidal fuller's earth clays when used as an animal litter is that they do not form clumps when exposed to urine, or, if they do, such clumps are not cohesive. The clumps, for example, formed by attapulgite LVM clay disintegrate completely when removed or dislodged. Another disadvantage is that they do not absorb the urine readily whereby the urine accumulates at the bottom of the litter box.
In order to improve the clumping and absorbing properties of fuller's earth clays, the clays are sometimes partially calcined to remove all or most of the free moisture thereof by heating them to a finishing temperature of not more than 180.degree. C. usually 120.degree. C. to 150.degree. C. Such clays are colloidal in that they form a colloid when exposed to or dispersed in a liquid environment such as an aqueous environment. In the case of attapulgite, the partially calcined clay is known as regular volatile material ("RVM") clay. In the case of bentonite, the clay is often only dried sufficient to allow grinding. Such clay has a free moisture of 6-8% upon standing.
All bentonite (smectite) clays swell to some extent in the presence of water. The swelling properties of bentonite are related to the arrangement of the exchangeable cations present in the particular bentonite. The principal cations are sodium, calcium and magnesium. Sodium bentonites can swell up to six times of their initial volume whereas calcium bentonites swell only slightly and magnesium bentonites swell about one half of their original volume. In commercial usage, a water-swellable bentonite is a sodium bentonite clay that hydrates in the presence of water, e.g., swells appreciably (six times or more of its initial volume) in the presence of water. On the contrary, in commercial usage, calcium and magnesium bentonites are not referred to as water swellable bentonites. One disadvantage of the water swellable bentonites is that, because of the significant swelling occurring upon their contact with water, they plug up the toilet when flushed. Therefore, they can not be disposed of in this manner.
U.S. Pat. No. Re. 33,983 discloses an animal litter containing water-swellable bentonite clay that is capable of agglomerating upon contact with a liquid animal dross. One presently available animal litter containing bentonite is one wherein the bentonite is sodium montmorillonite. That bentonite swells significantly when contacted with water and its disposal through flushing down the toilet is expressly not recommended by its manufacturer because it plugs it up. Another bentonite-containing litter presently available is one wherein the bentonite is calcium montmorillonite. That litter is flushable. One disadvantage thereof, however, is that it does not form cohesive clumps when it contacts animal urine.
U.S. Pat. No. 4,437,429 discloses an improved animal litter that includes a non-colloidal fuller's earth clay and an effective amount of a hydrated zeolite. One disadvantage of the animal litter disclosed in that patent is that the entire litter box must be disposed of after a certain period of time.
U.S. Pat. No. 4,085,704 discloses an animal litter that produces a continuous, long lasting, uniform, slowly released odor control agent. The patent discusses the addition of non-colloidal fuller's earth clay to the animal litter to reduce the cost of the litter.
U.S. Pat. No. 4,532,890 make reference to Japanese Patent Application Laid-Open No. 129622/1982 that discloses the use of zeolite as a deodorizer together with a bentonite. The bentonite used is non-colloidal bentonite.
The present invention discloses an animal litter that contains a montmorillonite clay which is economical and which forms strong clumps upon contact with the animal urine. That clay does not swell appreciably in water. Therefore, the clumps are easily disposable by flushing them down the toilet.
These and other objects and advantages of the present invention will become readily apparent from the following description.